Close to pulling the trigger on e30

Like the title states, oh so very close. I live in Iowa so (obviously) e85 is everywhere. My only real hesitations are economy and testing, this being my daily driver. Basically how much milage should I expect to be sacrificed to the corn gods when just driving it normally and should I be testing the e85 on every fill-up? I see you can get a gauge but it doesn't seem like most people do that.

Edit: finally came across the "Calling all e30 tunes" thread. I feel like this is a must read for anyone considering ethanol, a TON of good info in there. Hopefully this isn't a dumb question, would there be any harm in filling up 30 gals (I have 36 gal tank) and using a gauge to check the ethanol content, using the last 6 gallons to correct if necessary? I don't know why I am so against testing 😅